1. Technical Field
The embodiment relates to an exhaust gas control system for an internal combustion engine.
2. Description of Related Art
In an internal combustion engine mounted on a vehicle, or the like, there is known a technique for arranging a filter in an exhaust passage of the internal combustion engine in order to reduce emissions of particulate matter, emitted from the internal combustion engine, into the atmosphere. As a particulate matter accumulation amount in such a filter excessively increases, a pressure loss in the filter becomes excessive, with the result that back pressure that acts on the internal combustion engine increases. For this reason, when the difference (upstream-downstream differential pressure) between an exhaust pressure upstream of the filter and an exhaust pressure downstream of the filter is larger than or equal to a predetermined threshold, it is required to execute a process (filter regeneration process) for oxidizing and removing particulate matter accumulated in the filter by placing the surroundings of the filter in a high temperature and oxygen excessive atmosphere as needed.
The particulate matter that accumulates in the filter contains soluble organic fraction and soot. Even when the amount of particulate matter accumulated in the filter remains unchanged, the upstream-downstream differential pressure can vary depending on the ratio between the amount of soluble organic fraction and the amount of soot. For this reason, there is known the following method (see, for example, Japanese Patent Application Publication No. 2011-169235 (JP 2011-169235 A). In the method, a preprocess of oxidizing and removing soluble organic fraction accumulated in the filter by raising the temperature of the filter to a temperature at which soluble organic fraction oxidizes is initially executed, and then a process of oxidizing and removing soot accumulated in the filter by raising the temperature of the filter to a temperature at which soot is presumed to oxidize (a temperature higher than the temperature at which soluble organic fraction oxidizes) at the time when the upstream-downstream differential pressure in a state where soluble organic fraction has been removed is larger than or equal to a predetermined value is executed.